Plate heat exchangers with gaskets between the heat exchanger plates have been used in distillation plants for desalination of sea water for a long time. WO 2006/054936 discloses a distillation plant with such plate heat exchangers. Compared with tube heat exchanger, plate heat exchangers have several advantages. Most important is the compactness. The plate pack is smaller than a corresponding tube bundle. Since the plate pack respectively the tube bundle is placed in a vessel, a reduction of the size will influence the vessel size as well, which means a cost reduction for the vessel. The vessel cost is approximately proportional to the size in power two, so the effect of a size reduction is significant. Consequently the vessels for desalination plants are made as small as possible.
Another advantage with plate heat exchangers with gasketed packs of heat exchanger plates compared to tube bundles is the accessibility to the heat transfer surfaces. By untightening and taking the bolts away the pack can be opened and the heat exchanger plates are accessible. For a normal plate heat exchanger opening can be made in a couple of hours, and the plates can be cleaned and inspected hanging in the frame. It is not necessary to take them out from the frame. For a plate heat exchanger in a compact vessel it is more complicated. Due to the limited space it is not possible to do any service in the vessel, the plates must be taken out from the vessel, one by one, and that takes much longer.
In most big desalination plants there are several effects and each effect has at least one plate heat exchanger. Since all effects are necessary for the desalination process, maintenance of one plate heat exchanger stops the process. In order to reduce the downtime, the plant can have a spare plate heat exchanger, but the time for replacement is still unacceptable.